A simplified method for determining radiochemical purity of N-13 ammonia injection

372 Objectives: To develop a simple, rapid method to determine radiochemical purity (RCP) of N-13 ammonia injection using a solid phase extraction (SPE) method. Methods: Side-by-side comparative RCP tests were performed on 12 lots of N-13 ammonia injection, using a newly developed SPE based cationic exchange resin method and a HPLC method. The HPLC method utilized a Dionex CS12A column eluted with 20mM methane sulfonic acid. In-line conductivity and sodium iodide detectors were used. The SPE method was performed using a cation exchange column (Waters Accell™ Plus CM Sep-Pak®) primed with water and eluted sequentially with 3 mL of water and 3 mL of 2M CaCl2. N-13 ammonia is eluted with the calcium chloride solution. Radioactivity measurements of both eluates and the Sep-Pak® cartridge were performed in a CRC®-15 PET dose calibrator. Additionally, 11 samples of N-13 ammonia injection were spiked with unreacted N-13 NOX (0.9-14.7%) and assayed using the SPE method. Results: RCP (mean ± s.d., n=12) values were 99.27% ± 0.32% and 99.70% ± 0.28% for the SPE and HPLC methods, respectively. A paired t-test performed on these data shows no significant difference (P Conclusions: The SPE method is an acceptable method for the rapid determination of radiochemical purity in N-13 ammonia using readily available equipment and materials.